Method of testing cores

ABSTRACT

The loading capacity of a core manufactured by reeling and gluing from paper or board layers, is tested by dynamically loading the core under conditions that simulate real life conditions. The core is mounted on a chuck, and the method is practiced by loading the core by utilizing a roll that exerts a nip pressure, and by rotating the core. One or both of the loading and the speed of rotation of the core are changed over time in a predetermined manner, to simulate the real life conditions. For example the loading on the core can be increased constantly while the rotational speed is kept constant, or the rotational speed is increased and the loading decreased corresponding to the real use situation caused by unwinding of a paper roll which is mounted by the core. The method also includes detecting any changes in the structure of the core, either optically, by sensing vibrational changes, or by sensing the break of an electrical wire passing through the core. Loading is continued until the core breaks. One or both of the rotational speed of the core and the force loading of the core are sensed at the moment of change, and/or the time elapsed until the moment of change is detected. A sleeve may be provided on the core to contact the roll, the sleeve protecting the surface of the core and distributing the loading caused by the roll contact, to a wider area.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method of testing the loadingcapacity of cores. The method according to the invention is especiallysuitable for testing, for example, the strength of board cores used inthe paper industry.

Known cores used in the paper industry comprise several, for example25-30, thin, e.g. 0.5-1.0 mm, and narrow, about 100 to 200 mm wide,board tapes, which are joined by glueing and spirally winding by aspecial machine to form a tube-like product, which is used, for example,as a core of paper and plastic rolls.

Known methods for testing cores are almost completely based on statictesting. Examples of different types of methods in this group aremethods based on definition of radical compression strength, axialcompression strength, torsional strength, expansive strength, bendingstrength and like values. With these methods neither the loadingsituation nor the loading method corresponds the conditions which thecore encounters in reality. Additionally, the break mechanism effectedby said types of testing methods differs considerably from the breaksthat occur in reality. Such methods are also not capable of finding alldefects existing in the core, such as one insufficient glue seam or aweak board layer.

On the other hand, there are also a number of dynamic testing methodsfor cores, such as utilization of the vibration resulting from rotatingthe core on a test bench and loading of the core rotating on a chuckwith a belt. Although these methods are considerably better than theabove mentioned static methods due to their dynamics, even the dynamicmethods do not correspond accurately to loading situations. For example,the vibration in the test bench reflects a different characteristic thanthe loading strength of the core when rolling.

The various methods referred to above do not provide information withsufficient reliability and accuracy about the loading strength of boardcores in real rolling situations. Therefore a new type dynamic testingmethod for cores has been developed. The core is loaded in a mannercorresponding the real conditions of center winders and unwinding meansof printing presses, whereby the stress exerted on the core by theweight of the paper roll on the chuck can be simulated.

The method according to the present invention for testing the loadingcapacity of a core or the like member is characterized by mounting thecore on a chuck and dynamically loading the core by means of a roll tosimulate actual conditions of use wherein the loading of the core and/orthe rotational speed are changed relative to time in a predeterminedmanner until the core breaks; and detecting changes in the corestructure and recording the rotational speed and/or the force loadingthe core at the moment of change and/or the time elapsed at the momentof change.

The following advantages are obtained, for example, by the method and ofthe invention compared with known methods of testing cores:

a break mechanism as well as break surface end form correspond to realsituations;

the method detects even a slightest defect in glueing or board in thecore;

good correlation is effected in practice to the roll weights reached bydifferent core qualities;

stress and testing time of the core to be tested correspond better toreal life situations; and

the testing apparatus communicates with an automatic indicator of abreak point, and there is also direct reporting of the results.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of part of an apparatus for testingcores, applicable in the realization of a method in accordance with theinvention;

FIGS. 2a, b and c are graphs illustraing the testing principlesapplicable in the method according to the invention; and

FIG. 3 is a schematic partial view of the central parts of an apparatusfor practicing the method of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an apparatus for testing cores, which is mounted on abody construction 1. The testing apparatus comprises in principle threemain elements: a support apparatus 2 for the core to be tested, loadingapparatus 3 and a detector device 4 for detecting and indicating theeffects of the loading. The support apparatus 2 for the core includes asupporting installation 5 mounted on the body construction 1, a shaft 6mounted with bearings in the supporting installation 5. In thisembodiment a belt pulley or roller 7 is arranged on one end of theshaft, by which the shaft can be operated. On the other end of the shaftthere is a chuck 8, which can be varied and thus different types ofapparatus using cores can be simulated. The core 9 to be tested islocated on the chuck 8 a load sleeve 10 is also mounted on core 9 toprevent the loading apparatus 3 from breaking the surface of the core 9distributes the loading more uniformly on the surface of the core 9,exactly corresponding a real use situation. The chuck can be any type ofchuck commonly used in apparatus using cores, whereby it is alsopossible to study the force exerted by the chuck on the inner surface ofthe core.

The loading apparatus 3 includes a roller 11 for pressing the core 9 viathe load sleeve 10, which roller 11 is mounted with bearings on a shaft15 mounted on a carriage 14 slidable in the guide bars 13 of the body 12of the loading apparatus 3. The carriage 14 is vertically displaceableon the guide bars 13 and is connected by a bar 17 in the embodimentshown in the figure to the pneumatic cylinder 16 mounted on body 12 ofloading apparatus 3. A flange 18 is provided on roll 11 to prevent core9 and sleeve 10 from sliding off from chuck 8 in a loading situation.

The exemplary detector device 4 indicates the stress caused by theloading and comprises a light source 19, by means of which the edge ofthe core rotating on chuck 8 is illuminated, and a light detector 20,which measures the intensity of light reflecting from the edge of thecore. When during the loading of core 9 via load sleeve 10 by roll 11,for example, delamination of the board or opening of the glueing betweentwo board layers due to a glue fault occurs in the core a narrowrim-like gap is formed in the edge of the core, which gap does notreflect light to the detector, whereby the measuring device registersthe temporary pressure of roll 11 against load sleeve 10. Although aload sleeve is used on the core in the above example, which can be, forexample nylon, it is, of course, possible to load cores without asleeve, whereby the coating of the loading roll can be slightlyresilient, if required, so as not to make load stressing the coreexactly linear.

The vertical axis used in the coordinates of FIGS. 2a-c represents theloading (F) and the rotational speed (rpm) and the horizontal axisrepresents the time (t).

FIG. 2a represents a testing method, in which the loading is evenlyincreased and the rotational speed decreased. In other words a situationis illustrated, in which a paper web is reeled to a roll on a core, theloading against the core is at its minimum at the beginning and,respectively, the rotational speed at its maximum varying, when the rollis reeled, according to the figure. In principle, a corresponding figureis formed when the roll is unwound, thereby FIG. 2a is to be read fromthe right to the left.

FIG. 2b represents a testing method, in which the rotational speed isevenly increased and the loading is maintained constant during the wholetime.

FIG. 2c represents a testing method, in which the rotational speed ismaintained constant and the loading is increased. Such kinds ofexperiments also differ slightly from the usual loading conditions butare useful for testing some special cores. In addition to the abovedescribed measuring methods it is possible to study, for example, theeffects of a pulsating loading, because in practice there can sometimesbe vibrations in the reeling, which cause a pulsating loading. Accordingto the invention it is possible to provide a wholly automatic testingaction, typically by utilizing a microcomputer or microprocessor tocontrol or direct the testing. The utilization of a microcomputer ormicroprocessor with the heretofore described apparatus isstraight-forward and well within the skill of those in the art.

The apparatus for practicing the method according to the invention alsoincludes a data collecting or storage unit, which registers the stressdirected to the core via roll 11 and the rotational speed on the groundof the information coming from registration device 4 for the stresses.Such units are typically well known microprocessors, it is notconsidered necessary to give a detailed description of theirconstruction and operation. By connecting the measurements, for example,to be registered by a micro computer, it is possible to carry outnecessary calculations or other definitions at the same time. It ispossible to define a force or weight which breaks the core for everytype of a core to be tested by determining by calculation thecorresponding weight from the value of the loading strength.

It is also possible to determine a core suitable for a particularpurpose on the basis of a core of particular size and strength. In otherwords, when the strength directed against the core in the object of useis knowm, it is possible on the basis of practical knowledge tocalculate the core type presumably suitable for the particular purpose.

By carrying out the testing according to the invention, it can bedetermined whether the type of core tested is exactly suitable, orwhether it is possible to choose a less expensive and/or somewhat weakercore, or whether a next larger size should possibly be chosen. Thus themethod according to the invention enables the selection of the mostsuitable core for the user for each purpose without a risk of breakingthe core.

As is to be noted from the above description there is developed a newtype of testing method for cores, which is simple, but at the same timereliable and which can accurately simulate real life situations.However, while only one embodiment described in detail is introducedabove, the inventive concept includes many different modificationswithin the scope of invention defined by the accompanying claims. Thusit is possible to alternatively arrange a loading roll to be used,whereby it alone would revolve the sleeve, the core and the chuck withthe shaft. Furthermore, it is possible that both said members might beused at the uniform speed, whereby the frictional effects or factors canbe eliminated or minimized. As for the observation equipment, it canalso differ from the above described which should only be considered anexample of a device generally operating optically. Other possiblealternatives are various vibration bulbs, which indicate the moment whena radical change in the core takes place, such as a tear in some of thecardboard layers, or the loosening of the glueing between the layers.Additionally, it is possible to arrange a thin wire leading an electriccurrent across the layers, whereby the rupture of the bonding betweenthe layers and the sliding of the layers relative to each other causesthe breaking of the wire and thus an easily registrable alarm. Ofcourse, it is possible and in some cores sufficient to effect visualobservation such as with a stroboscope, whereby the equipment is nottotally automatic, as it can be in the other described embodiments. Thiskind of observation is also not very reliable and quick, but it can besufficient in some embodiments of the applications of the method inaccordance with the invention. Finally, it should be noted that althoughthe method according to the invention is described in testing cores, itcan be applied just as well in testing other products of same form andsubject to similar stress.

We claim:
 1. A method of testing, by dynamic loading simulating reallife conditions, the loading capacity of a core manufactured by reelingand gluing from paper or board layers, the core mounted on a chuck, andutilizing a roll, said method comprising the steps of:(a) loading thecore mounted on a chuck by exerting a nip pressure on the core with theroll; (b) rotating the core in contact with the roll; (c) changing oneor both of the loading and rotational speed over time in a predeterminedmanner; and (d) detecting any changes in the structure of the core.
 2. Amethod as recited in claim 1 comprising the further step (e) ofdetecting one or both of the rotational speed of the core and the forceloading on the core at the moment of a change in the core.
 3. A methodas recited in claim 2 wherein step (c) is practiced by constantlyincreasing the load on the core until the core breaks.
 4. A method asrecited in claim 1 comprising the further step of detecting orregistering one or both of the rotational speed of the core and theforce loading on the core of the time elapsed until the moment of achange in the core.
 5. A method as recited in claim 4 wherein step (c)is practiced by constantly increasing the load on the core until thecore breaks.
 6. A method as recited in claim 1 comprising the furtherstep (e) of detecting one or both of the rotational speed of the coreand the force loading on the core at the moment of change in the core,and the time elapsed until the moment of change in the core.
 7. A methodas recited in claim 6 wherein step (c) is practiced by constantlyincreasing the load on the core until the core breaks.
 8. A method asrecited in claim 1 utilizing a light source and an end face of the core,and wherein step (d) is practiced by optically detecting light reflectedfrom the light source off the end face of the core.
 9. A method asrecited in claim 8 utilizing a sleeve mounted on the core for protectingthe surface of the core and distributing the loading caused by the rollto a wider area, and wherein step (a) is practiced by the loading thecore by contacting the sleeve with the roll.
 10. A method as recited inclaim 1 wherein step (d) is practiced by sensing the vibration caused bya change in the structure of the core.
 11. A method as recited in claim1 wherein the core is layered, and utilizing an element leading anelectric current across the layers of the core; and wherein step (d) ispracticed by sensing a break in the electric current carrying member.12. A method as recited in claim 1 wherein step (c) is practiced byconstantly increasing the load on the core until the core breaks.
 13. Amethod as recited in claim 12 wherein step (c) is practiced byincreasing the load on the core at a rate that corresponds to the realgrowth speed of the weight the core will be subjected to during actualuse.
 14. A method as recited in claim 12 wherein step (c) is practicedso that the loading on the core is increased at a rate that is higherthan the real growth speed of the weight loading that a core will besubjected to in actual use.
 15. A method as recited in claim 12 whereinstep (b) is practiced by keeping the rotational speed of the coreessentially constant.
 16. A method as recited in claim 12 utilizing asleeve mounted on the core for protecting the surface of the core anddistributing the loading caused by the roll to a wider area, and whereinstep (a) is practiced by the loading the core by contacting the sleevewith the roll.
 17. A method as recited in claim 1 wherein step (c) ispracticed to change the rotational speed of the core as a function oftime corresponding to the slowdown of the rotational speed of the coreduring actual use of the core.
 18. A method as recited in claim 1wherein step (c) is practiced by increasing the rotational speed of thecore and decreasing the loading on the core to corresponding to a realuse situation caused by the unwinding of a paper roll associated withthe core.
 19. A method as recited in claim 1 utilizing a sleeve mountedon the core for protecting the surface of the core and distributing theloading caused by the roll to a wider area, and wherein step (a) ispracticed by the loading the core by contacting the sleeve with theroll.